Hepatocyte growth factor (HGF), also known as scatter factor (SF), is a growth factor which is involved in various physiological processes, such as wound healing and angiogenesis. The high affinity interaction of HGF interaction with its receptor (c-Met) is implicated in tumour growth, invasion and metastasis.
Knudsen et al have reviewed the role of HGF and c-Met in prostate cancer, with possible implications for imaging and therapy [Adv. Cancer Res., 91, 31-67 (2004)]. Labelled anti-met antibodies for diagnosis and therapy are described in WO 03/057155, EP 2127683 A1 and WO 2011/110642.
c-Met has been shown to be involved in tumour growth, invasion and metastasis in many human cancers of epithelial origin. c-Met is expressed by most carcinomas and its elevated expression relative to normal tissue has been detected in cancers of: lung, breast, colorectal, pancreatic, head and neck, gastric, hepatocellular, ovarian, renal, glioma, melanoma and a number of sarcomas. In colorectal carcinoma (CRC), over-expression of c-Met has been detected in dysplastic aberrant crypt foci, the earliest pre-neoplastic lesions of the disease. In head and neck squamous cell cancer, c-Met is reportedly expressed or overexpressed in roughly 80% of primary tumours. In prostate cancer metastasis to bone, c-Met was reported overexpressed in over 80% of bone metastases.
Under normal conditions, c-Met is expressed on epithelial cells and activated in a paracrine fashion, by mesenchymally derived HGF. The activation of c-Met in normal cells is a transient event and is tightly regulated. In tumour cells, however, c-Met can be constitutively active. In cancer, aberrant c-Met stimulation can be achieved through c-Met amplification/over-expression, activating c-Met mutations (e.g. structural alterations) and acquisition of autonomous growth control through creation of autocrine signalling loops. In addition, a defective down-regulation of the c-Met receptor will also contribute to aberrant c-Met expression in the cell membrane. While the over-expression of c-Met is HGF dependent (autocrine/paracrine), structural alterations caused by mutations are HGF independent (e.g. loss of extracellular domain).
WO 2004/078778 discloses polypeptides or multimeric peptide constructs which bind c-Met or a complex comprising c-Met and HGF. Approximately 10 different structural classes of peptide are described. WO 2004/078778 discloses that the peptides can be labelled with a detectable label for in vitro and in vivo applications, or with a drug for therapeutic applications. The detectable label can be: an enzyme, a fluorescent compound, an optical dye, a paramagnetic metal ion, an ultrasound contrast agent or a radionuclide. Preferred labels of WO 2004/078778 are stated to be radioactive or paramagnetic, and most preferably comprise a metal which is chelated by a metal chelator. WO 2004/078778 states that the radionuclides therein can be selected from: 18F, 124I, 125I, 131I, 123I, 77Br, 76Br, 99mTc, 51Cr, 67Ga, 68Ga, 47Sc, 167Tm, 141Ce, 111In, 168Yb, 175Yb, 140La, 90Y, 88Y, 153Sm, 166Ho, 165Dy, 166Dy, 62Cu, 64Cu, 67Cu, 97Ru, 103Ru, 186Re, 203Pb, 211Bi, 212Bi, 213Bi, 214Bi, 105Rh, 109Pd, 117Sn, 149Pm, 161Tb, 177Lu, 198Au and 199Au. WO 2004/078778 states (page 62) that the preferred radionuclides for diagnostic purposes are: 64Cu, 67Ga, 68Ga, 99mTc and 111In, with 99mTc being particularly preferred.
WO 2008/139207 discloses c-Met binding cyclic peptides of 17 to 30 amino acids which are labelled with an optical reporter imaging moiety suitable for imaging the mammalian body in vivo using light of green to near-infrared wavelength 600-1200 nm. The c-Met binding peptides comprise the amino acid sequence:
Cysa-X1-Cysc-X2-Gly-Pro-Pro-X3-Phe- Glu-Cysd-Trp-Cysb-Tyr-X4-X5-X6;                wherein X1 is Asn, His or Tyr;                    X2 is Gly, Ser, Thr or Asn;            X3 is Thr or Arg;            X4 is Ala, Asp, Glu, Gly or Ser;            X5 is Ser or Thr;            X6 is Asp or Glu;and Cysa-d are each cysteine residues such that residues a and b as well as c and d are cyclised to form two separate disulfide bonds. The optical reporter of WO 2008/139207 is preferably a cyanine dye.                        
WO 2009/016180 discloses c-Met binding cyclic peptides analogous to those of WO 2008/139207, wherein the optical reporter is a benzopyrylium dye. The agents of WO 2008/139207 and WO 2009/016180 are stated to be useful for in vitro and in vivo optical applications, especially optical imaging in vivo of the human body. Optical imaging of colorectal cancer is a preferred application.
WO 2011/020925 discloses anti-c-Met antibodies and uses thereof. WO 2011/020925 discloses that the antibodies can be used to help determine the susceptibility of a patient to treatment with anti-c-Met antibodies. The method involves the use of an in vitro method (immunohistochemical analysis of a tumour sample) to determine the c-Met status of a tumour. This method still, however, relies on biopsy with the disadvantages described above.
Merchant et al [2011 ASCO Meeting; J. Clin. Oncol., Abstract 10632, Suppl. (2011)] disclose an anti-c-Met antibody (MetMab™) labelled with 76Br or 89Zr— for molecular imaging of c-Met in mouse xenografts. The agents were reported to exhibit rapid tumour uptake and slow clearance.
Drug chemotherapeutic agents directed at c-Met (“anti-Met therapies”) are in development by a number of organisations. Such agents are expected to be used typically in metastatic disease. Clinical results to date, however, suggest that patient prognosis is dependent on knowledge of the c-Met status of the tumour. It is also possible that c-Met status could be predictive of response to anti-c Met therapies. Currently, the c-Met status can be determined by immunohistochemical (IHC) analysis of a biopsy sample taken from the patient, but biopsy is invasive (carrying some risk to the patient), and may not result in a representative sample. Thus, there is an inherent risk of sampling error where mainly healthy tissue is collected, or due to tumour heterogeneity, a section of the tumour that is unrepresentative of the molecular profile for the most active part of the tumour is taken [N. Engl. J. Med., 366(10); 883-892 (2012)]. In addition, biopsy provides information only on the tumour sampled—not the patient's tumour and/or tumour metastasis burden as a whole. Since anti-Met therapy is expected to be used as a second- or third-line therapy, biopsy material of satisfactory quality representative of the untreated tumour may be unavailable, or could potentially no longer be representative for the molecular profile of the tumour. Resampling via biopsy is generally not carried out, as it carries some risk of morbidity, as well as due to the issues described above.
In a recently published study [Cancer Discovery, 1(1); 44-53 (2011)], the value of obtaining new biopsies in pre-treated NSCLC patients with advanced disease (n=139) and utilizing real-time biomarker analyses for selection of treatment was explored. It was found that allocating patients to treatment based on the molecular profile increased the probability of a positive treatment outcome. Though the biopsy procedure reportedly was well-tolerated in the trial, pneumothorax occurred in 11.5% of the patients, leading to the conclusion that although re-biopsying patients for treatment stratification based on biomarkers is advantageous, it is not without risk.
In a Phase II trial for MetMAb™, a monoclonal antibody blocking c-Met (Roche) [2011 ASCO Annual Meeting & http://www.roche.com/media/media_releases/med-cor-2011-05-19.htm], NSCLC patients were randomised to either:                (i) MetMAb+Erlotinib (EGFR inhibitor; or        (ii) placebo+Erlotinib.c-Met status was determined by IHC and FISH analyses of archive samples (approximately 50% were positive by IHC). In the patient group as a whole (i.e. including patients with high and low c-Met expression), there were no differences between the two treatments. When the data were analysed, based on retrospective IHC analysis of archive biopsy samples, the median overall-survival was 12.6 months in the MetMAb group vs 3.8 months in the Erlotinib group (p=0.002). In addition, the patients with low c-Met expression treated with MetMAb in combination with Erlotinib had a worse outcome compared to Erlotinib alone. Prospective collection of biopsies prior to treatment was not included in the trial, and it is unknown if the c-Met scoring based on the archive samples was fully representative for the study population. Oliner et al. [J Clin Oncol 30, Suppl., abstr 4005 (2012)] recently published data for a Phase 2 study of the HGF antibody, rilotumumab (Amgen), in combination with epirubicin, cisplatin, and capecitabine (ECX) in patients with locally advanced or metastatic gastric or esophagogastric junction cancer. Patients with c-Met high tumours (>50% tumour cells positive) had improved median overall survival when treated with the combination therapy compared to patients treated with placebo and ECX. Conversely, patients with c-Met low tumours (≤50% positive) had a trend toward unfavourable overall survival when treated with the combination therapy compared with those treated with placebo and ECX. In the placebo and ECX group, patients with c-Met high tumours had poorer overall than patients with c-Met low tumours.        
There is therefore a need for a less invasive method of assessing the c-Met status of the tumour and/or tumour metastasis burden of a patient, to determine whether the individual patient would benefit from anti-Met therapy.
The Present Invention.
The present invention provides a method of determining the c-Met status of patient's tumour(s), to assist in the decision process before initiation of c-Met therapy in cancers such as, NSCLC, colorectal cancer (CRC) and gastric cancer. For anti-Met therapy, a treating physician would need to know the c-Met status of the patient (tumour and metastases) before initiating adjuvant c-Met inhibitor therapy. For a newly diagnosed patient it may be possible to get the answer from molecular analysis of the diagnostic biopsy, but for patients that have failed on standard therapy, if any archive sample is available it may not be fully representative of the current status of the disease.
The method of the present invention assists the physician in determining when an individual patient would benefit from anti-Met therapy. Importantly, the method also helps to exclude from such treatment patients where anti-Met therapy would either be ineffective, or have a negative effect.
The method of the present invention carries much less risk to the patient than biopsy, and has the advantage of providing a way of assessing total c-Met burden for all tumours and metastases—including e.g. the expression of tumour sites that are difficult to biopsy, or sites of previously unknown metastasis. It therefore gives a more complete picture for the patient than analysis of biopsy samples (even assuming such samples are available). In addition, the method lends itself to repeat imaging at different time intervals, so can be used to monitor anti-Met therapy.
MetMab™ exhibits a combined elimination half-life of 8-12 days, so does not have ideal pharmacokinetics for in vivo imaging—since clearance from background would be extremely slow. In contrast, the agents of the present invention permit imaging within 1 hour of administration to the patient.
The present invention also provides a means for monitoring anti-Met therapy. This is expected to be of significance in either determining that a given therapy is proving successful for an individual patient (and is hence worth continuing), or is not efficacious—permitting an earlier change to a different treatment or medication.